Usually during factory setting the basic brightness of a monochrome panel is set via the so-called offset of an A/D converter in such a way that a video step 0 is generated from the lowest video level of 0 volts of an analog image signal when a black image is displayed on the panel. If the brightness is set too low, this will result in an excessively dark image, as it is only, for example, at a video level of 0.1 volts at the A/D converter input that a video step greater than 0 is produced at its output, thereby causing image information and levels of grey to be lost. On the other hand, if the brightness is set too low, an excessively light image will result. In this case, for example, at a video level of 0 volts a video step 32 is generated instead of a video step 0, likewise causing image information and levels of grey to be lost.
Also during factory setting the contrast of the monochrome panel is set via the gain of the A/D converter in such a way that a maximum video step is generated from the highest video level, e.g. a video level of 0.7 volts, of an analog image signal when a white image is displayed on the panel. Should, for example, an 8-bit A/D converter be provided, the gain is set in such a way that this A/D converter generates a video step 255 from the maximum video level 0.7 volts. If the contrast is set too low, this produces an excessively low-contrast image and levels of grey are lost, as the A/D converter does not produce the maximum possible video step from a maximum video level. On the other hand, if the contrast is set too high, this causes the A/D converter to output the maximum video step even before the maximum video level is attained, causing image information to be lost.